Fail-safe permanent magnet lifting device with a movable bias keeper



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3,389,356 FAIL-SAFE PERMANENT MAGNET LIFTING DEVICE WITH A MOVABLE BIAS KEEPER William Schneider, Pittsburgh, Pa., assignor to American Chain & Cable Company, Inc., New York, NX., a corporation of New York Filed Aug. 23, 1965, Ser. No. 481,552 3 Claims. (Cl.y 335-289) lThis invention relates to an improved permanent lifting device and more particularly to a permanent magnet lifting device wherein the permanent magnets, control coil and center pole are secured in a rigid rectangular enclosure comprising a pair of side Walls and a pair of nonmagnetic end walls and wherein the lifting forces are carried lby the plates forming the center pole of the magnetic lifting device.

There is disclosed in U.S. Patent 3,316,514 entitled Fail-Safe Electro-Magnetic Lifting Device With Safety Stop Means, a fail-safe lifting device wherein a pair of elongated permanent magnets are magnetically lsecured to a center pole and end poles of magnetic material. A control coil is wound about a portion of the center pole and serves to transfer -flux by current reversal through a movable upper keeper plate that abuts the upper edge surfaces of the poles and a lower keeper plate, i.e., the load lifted by the lifting device. Secured to the side walls ofthe end plates are nonmagnetic stop members that limit the upward movement of the upper keeper plate relative to the upper edge surfaces of the side plates. The keeper plate has a suitable connecting device secured thereto that supports the load in an elevated position. Thus the lifting forces are carried by the keeper plate.

The fail-safe permanent magnet lifting device disclosed in the above named application functions in the following manner. When the permanent magnet flux by means of the control coil is transferred toward the bias keeper plate positioned above the control coil the keeper plate is magnetically secured to the end plates or poles and center pole. If the lower surface of the lifting device with this magnetic flux path is brought in contact with a metallic plate the magnetic lifting device will not lift the load i.e. the major flux path is through the movable upper keeper plate. To pick up a metallic magnetizable plate the magnetic lifting device is lowered to bring the lower edge portions into abutting relation with a surface of the plate. A pulse of current is sen-t through the control coil in the opposite direction and transfers the major magnetic ilux path from the upper bias keeper plate through the lower metallic plate. The pulsek of reverse current thus releases the magnetic force previously exerted on the upper bias keeper plate.

When the magnetic device is lifted the bias keeper plate first moves upwardly against the stops of the nonmagnetic material secured to the end plates. This provides an air gap between the bias keeper plate and the poles of the magnet. The magnetic flux path in this position extends through the end poles, and the magnetic plate or load that is being lifted.

lf, in an elevated position where the bias keeper plate is spaced from the poles of the magnet, a pulse of current is laccidentally sent through the coil to reverse the flux path and release the load, the air gap between the bias plate and poles of the magnet prevents the flux path from changing so that the load remains magnetically secured to the lifting device. To disengage the `load from the lifting device it is necessary to first lower the load and permit the bias keeper plate to move into abutting relation with the poles of the magnet. A pulse of current sent through the control coil in a proper direction Will then change the major `lux to extend through the keeper plate that forms a part of the lifting device and thus disengages theload.

United States Patent O 3,339,356 Patented June 18, 1968 ICC Although the above described magnetic lifting device has provided a fail-safe means for lifting metallic articles of magnetizable material, problems have been encountered in the fabrication of the elements and their .assembly to provide optimum operation. For example, it has been discovered that the sandwich formed by the magnetic pole pieces and the permanent magnets, although attracted to each other magnetically tend to move relative to each other and fail to provide a planar undersurface for contact with magnetizable articles. The presence of even minute air gaps between the pole pieces and the load reduces to a great extent the load capacity of the lifting device. Where the pole pieces and permanent magnets become misaligned because of abuse in handling the lifting device, air gaps between the pole pieces and the load are inherent.

Another problem has been encountered in obtaining optimum characteristics of the permanent magnet. In the past it has been the practice to magnetize the permanent magnet material and then remove it from the magnetizer. In this condi-tion the permanent magnet material is open circuited :and has no magnetic circuit other than the circuit found within itself. The permanent magnet material in this condition has a unit permeability return path of indeterminate length and cross section which results in pole faces of the magnet exerting a self-impressed and severe demagnetizing effect on itself. It has been discovered by magnetizing the permanent magnet material with a pair of metallic keeper plates on opposite faces thereof a magnetic circuit is provided for the permanent magnets that minimizes the loss in the magnetic properties obtained during magnetization. The keeper plates utilized during magnetization of the permanent magnets further serve as spacer plates in the lifting ldevice for optimum spacing -of the pole faces and remain with the permanent magnet during shipment, storage and the like. With this Iarrangement the magnetic circuit for the permanent magnet positioned between a pair of keeper plates is the same as in the assembled magnetic lifting device.

With :the above described rigidiiied construction of the permanent magnets and pole pieces it is now possible for the center pole pieces to carry the load. The rigid enclosure for the permanent magnets, control coil and center pole pieces provide a structure that has high shear l l strength and the previously present bending moment on the keeper plate is eliminated. The shear forces of the load can therefore be transferred directly in-to the center pole pieces of the rigid lifting device.

Accordingly, the principal object of this invention is to provide an improved permanent magnet lifting device wherein the permanent magnets and control coil are positioned in a rigid enclosure comprising nonmagnetic sections and magnetic side sections that serve as end pole l pieces for the lifting device.

Another object of this invention is to provide a mag-r netic lifting device wherein the lifting forces are transferred linearly into the center of the magnetic lifting device.

Another object of this invention is to provide a pair of keeper plates for the permanent magnet that stabilizes the permanent magnet material upon removal from the magnetizerand serve as spacer plates in the magnetic lifting device.

yThese and other objects and advantages of this invention will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

ln the drawings:

FIGURE 1 is anend view of my improved permanent magnet lifting device illustrating the keeper plate in a lowered position abutting the upper faces of the pole pieces.

FIGURE 2 is similar to FIGURE l illustrating the keeper plate in spaced relation to the upper faces of the pole pieces.

FIGURE 3 is an exploded isometric View with portions broken away for illustrative purposes illustrating the various elements of my improved permanent magnet lifting device.

FIGURE 4 is a fragmentary view in elevation illustrating the bias keeper plate abutting the center pole pieces and the guiding and lifting bolt and bushing.

HGURE 5 is similar to FEGURE 4 illustrating the keeper plate abutting the undersurface of the bolt head in spaced relation to the pole pieces.

FIGURE 6 is a View in section of another lifting arrangement for my magnetic lifting device wherein the bias keeper plate is formed in two sections hingedly secured to the end poles and movable relative to the center pole by means of the lifting hook.

FIGURE 7 is a view similar to FGURE 6 wherein the lifting hook has pivoted the sections of the bias plate t lifting device generally designated by the numeral 10. f

The lifting device has a pair of elongated permanent magnets 12 and 14 that are each sandwiched between metallic keeper plates 15 and 18. The keeper plates 16 and 18 are magnetically soft so that the flux path of the permanent magnet is conducted therethrough. As will be later discussed, the permanent magnet material is sandwichedkbetween the keeper plates 16 and 13 before the permanent magnet material is magnetized in a suitable magnetizer and serve as spacer plates for the lifting device 16.

A pair of steel center plates 20 and 22 fabricated from a magnetically soft material that carry but do not retain a magnetic flux are positioned in abutting relation to each other and form the center pole for the magnetic lifting device lt?. The plate 20 has a pair of threaded apertures 24 and 26 formed in each end wall and another threaded aperture 2S formed in its upper wall. The plate 22 also has a pair of threaded apertures and 32 in each end wall and a vertical threaded aperture 34 in the top wall.

A pair of steel end plates 36 and 38 also fabricated from magnetically soft .material have spaced threaded apertures 4@ in the end walls and are positioned on opposite sides of the permanent magnets 12 and 14. The steel end plates 36 and 3S serve as end pole pieces for the magnetic lifting device 1d. The permanent magnets 12 and 14 and keeper plates 16 and 18 have an upper surface that terminates below the upper edge or surface of the end plates 36 and 38. A coil 42 is wound about the center poles or plates 20 and 22 and has suitable leads extending to the control box generally designated by the numeral 44.

A pair of passageways or bores 46 and 48 extend through the end plates 36 and 3S, the center plates 2t) and 22, the permanent magnets 12 and 14, and the keeper plates 16 and 18. A pair of elongated bolts similar to bolt 50 have threaded end portions and extend through the respective bores 46 and 48. Nuts 52 are positioned on the threaded end portions of bolts Si) and serve to rigidly secure the components of the magnetic lifting device 10 to each other. The end plates 36 and 38 because of the compressive forces exerted thereon by the nuts 52, fixedly position the components previously described therebetween.

The end plates 36 and 3S and center plates 2G and 22 are so dimensioned that the upper surfaces of the respective plates are in substantially the same horizontal plane. Similarly the lower edge portions of the plates 36 and 38 and center plates 2t) and 22 are so dimensioned that they are in substantially the same horizontal plane. The center plates 2t) and 22 serve as center poles of the magnetic .4- lifting device and the end plates 36 and 38 serve as end poles of the magnetic lifting device 1d. The plates 20 and 22, plates 36 and 38 and 16 and 18 are preferably fabricated of a magnetically soft material that is capable of carrying but not retaining a magnetic iiux.

End plates S4 and 56 fabricated from a nonmagnetic material each have a plurality of apertures 57 therethrough that mate with the respective apertures 49 in plates 36 and 38 and apertures 24 and 26 in center plates 2@ and 22. The end plates 54- and 56 are positioned in abutting relation with the end surfaces of plates 36 and 3S and are rigidly secured thereto by suitable screws 59 extending through the mating apertures as is illustrated in FGURES 1 and 2.

The end plates S4 and 56 and the side plates 36 and 33 form a rigid rectangular enclosure for the permanent magnets 12 and 14 and the center plates 20 and 22. Thus with the end plates 54 and 56 and the bolts 50 extending through the various components above described there is provided a sub-assembly for my permanent magnet lifting device 1t)` that is rigid with a planar undersurface that is not subject to distortion under load conditions and thereby eliminates any air gaps between a planar surface of an article that is being lifted and the abutting surfaces of the magnetic lifting device.

Although the permanent magnets 12 and 14 do magnetically secure the center poles 26 and 22 and end poles 36 and 38 thereto by magnetic forces it has been found that abuse to the magnetic lifting device requires a rigid structure to maintain the various elements in proper relation to each other.

The coil 42 is connected to a suitable source of DC current within control box 44. It has been found that a 6 volt dry cell battery is sufficient to provide the necessary pulse of current for the switching operation. The source of DC current is connected to the coil through a switching device that is arranged to reverse the direction of current flow for the purposes later described.`

The bias keeper plate 58 has a preferably planar undersurface that is arranged to abut the upper surfaces of the end poles 36 and 38 and the center poles 20" and 22. The keeper plate 5:8 is fabricated of a magnetically soft material that carries but does not retain a magnetic flux. The keeper plateS has a pair of upwardly extending connectors 60 and 62 which are connected to a lifting clevis 64 by means of Ia pin 66. The keeper plate 58 has a pair of apertures 68 and '70 therethrough in which are positioned bushings 72 fabricated of a nonmagnetic material. The apertures 63 and 70 are aligned with the apertures 28 and 34 in the center plates 20 and 22.

Bolts 74 have a threaded end portion 76, a cylindrical intermediate portion 78 and an enlarged head portion 80. The bolts 74 extend through the bushing 72 and are threadedly secured in the respective apertures 28 and 34 in center plates Ztl and 22. The intermediate portion 78 is so dimensioned that the bushing '72 is freely movable axially thereon. The bolts 74, therefore, secure the bias keeper plate 58 to the center plates Ztl and 22 in a manner that the bias keeper plate 58 is movable a preselected distance away from the surfaces of the end plates 36 and l3S and center pl-ates20 and 22.

It will be apparent with the above described arrangement that the lifting forces exerted -on the lifting clevis 64 is transmitted linearly from the bias keeper plate 58 to the center plates 2t) and 22. The center plates 20 and 22 are in turn rigidly connected to the rigid enclosure formed by the plates 36 and 38 and the end plates 54 and S6 to thereby distribute the shear forces exerted on the lifting device uniformly throughout the various components and to maintain a rectangular configuration with the planar edge surfaces previously discussed. The arrangement of the bolts T4, bushing 72, keeper plate 58 and center plates 20 and 22 is illustrated in detail in FIGURES 4 and 5.

The above described lifting device 10 functions in the following manner. The end plates 36 and 38 which are fabricated of a magnetic material serve as end poles for the magnetic circuit. The center plates 20 and 22 are also fabricated of a magnetic material and serve as center poles for the magnetic circuit. The faces of the end pole -36 and center pole v20 are in conducting relation with permanent magnet 12 and serve as part of a magnetic circuit. Similarly, the faces of end pole 38 and center pole 22 are in conducting relation with permanent magnet 14 and serve as part of another magnetic circuit. The coil 42 Wound about the center poles 20 and 22 serves as a switching means that -transfers the magnetic flux from a circuit through the bias keeper plate to va circuit through the load to be carried by the lifting device. The bias keeper plate 58 is arranged to abut the surfaces of the end poles 36 and 38 and center poles 20 and 22. The bias keeper plate 58 is also fabricated from a magnetic material so that when it is in abutting relation with the upper surfaces of the end poles 36 and 38 and center poles 20 and 22 a pair of ux paths may be completed therethrough. For example, a flux path is completed from t permanent magnet .12 through end pole 36, keeper plate 58 and center pole 20. Similarly, a flux path is completed from permanent magnet 14 through end pole 38,

keeper plate 58 Land center pole 22.

A second keeper (load) is indicated in FIGURE l by the numeral 82. Thus any element having a planar surface fabricated from a magnet material may be lifted by the permanent magnet lifting device 10. For illustrative purposes a plate 82 is illustrated as the load to be lifted by the permanent magnet lifting device. To lift the load 82 the permanent magnet device 10 is lowered onto a surface thereof until the underside of the center poles 20 and 22 and end poles 36 and 3=8 are in abutting relation therewith. A p'ulse of current is sent through the coil 42 from the source of current `44 in the proper direction to create a flux path from permanent magnet 12 through end pole 36, load 82 and center pole 20. A second flux path or circuit is created from permanent magnet 14 through end pole 38, load 82 and center pole 22. Thus the load 82 is magnetically secured to the respective end poles and center poles by the p'air of flux paths or circuits. As the permanent magnet lifting device is elevated by means of a crane or the like, the clevis device 64 and the keeper plate 58 move upwardly on the bolt cylindrical portions 718 until the keeper plate abuts the under surface of the bolt head 80. In this position there is an air gap between the bias keeper plate 58 and the up'per surfaces of end pole's 36 Iand 38 and center poles 20 and 22. Further upward movement of the lifting device 10 elevates the load 82 that is magnetically secured to the end poles 36 and 38 and center poles 20 and 22. In this elevated position there is an air gap between the bias keeper plate 58 and the upper surface of the end poles and center pole. The air gap between the keeper plate 58 and the poles of the permanent magnet lifting device prevent an accidental switching of the flux path from the load 82 to the keeper plate y58. 'Io release the load it is necessary to lower the load until the keeper plate moves into abutting` relation with the surfaces of the poles.

The load forces in the above described permanent magnet lifting device are equally distributed through all of the elements thereof by the rigid rectangularenclosure formed by the side walls 36 and 38 land end walls 54 and 56. Further, the bolts 50 maintain the elements of the lifting device in proper relationship with each other to retain a planar undersurface that abuts the load without having air gaps therebetween. The load forces are carried by the center pole-s and 22 so that distortive forces are not exerted on the lifting device. The load forces are substantially linear between the clevis 64 and the permanent magnet center poles 20 and 22.

There is illustrated in FIGURES 6 and 7 an arrangement for movin-g the bias keeper plate away from the center poles. The embodiment illustrated in FIGURE 6 includes a pair of center poles 100 and 102 with a coil 104 Wound around the upper portion thereof in a manner .similar to that illustrated in FIGURE 3. The end poles 106 and 10S lare similar to the end poles 36 and 38 previously described. The center poles and 102 are maintained in abuttin 7 relation to each other by means of bolts similar to the bolts 50 and have a plurality of chambers 110 only one of which is illustrated. The chamber 110 has a lower wall 112 and an upper wall 114. A recessed portion 116 is formed in the upper surface of poles 100 and 102 and a passageway 118 connects the chamber 110 and the recessed portion 116.

The bias keeper plate is formed in two elongated sections or halves 120' and 122. The section 120 is hingedly secured to the end pole 106 by a hinge 124 and section 122 is similarly secured to end pole 108 by hinge 126. The sections 120 and 122 have a plurality of co-opera-ting semicircular apertures 128 and 130 that are positioned above the recessed portion 114 and passageway 118 in the center poles 100 and 102. A plurality of hook members 132, only one of which is shown, have a stem 134 extending downwardly therefrom. The stem 134 has an abutment 136 and a lower spaced abutment member 138. The lifting device is assembled with the abutment lower member 138 of hook 132 positioned in chamber 110 and upper abutment member 136 in recess 116.

When the lifting device is resting on a surface and an upward lifting force is not being exerted on hook 132 the hook abutment member 138 abuts the bottom wall 112 of chamber 110 and the abutment member 136 extends into recess 116. In this position the sections or halves 120 and 122 of the bias plate abut the center poles 100 and 102 so that a magnetic circuit can be completed through end pole 106, bias plate sections 120 and 122 and center poles 100 and 102. When a lifting force is exerted on the hook 132 the lower abutment member 138 moves upwardly into abutting relation -with the chamber top surface 114 so that further upward movement of the hook 132 will move the lifting device therewith. In the lifting position illustrated in FIGURE 7 the upper abutment member 136 moves the bias keeper sections 120 and 122 away from the center poles 100 and 102 to open the circuit between the center poles 100 and 102 and end poles 106 and 10S. The halves or sections of the bias keeper hing- `edly pivot about the respective hinged connections 124 and 126. With this arrangement the circuit between the end poles and the center pole is opened by the air gap or spacing between the keeper plate sections 120 and 122 and the center poles 100 and 102.

A suitable permanent magnet for use in the above described lifting apparatus may be fabricated from a ceramic barium ferritematerial having a coercive force of about 2200 oersteds and a residual induction of 400() gausses. Suitable permanent magnets may be purchased from the Indiana General Corporation under the trade name of IndoX #'5, or from Westinghouse Electric Corporation under the trade name Westro Alpha. The keeper plate and pole pieces may be fabricated from a cold roll steel designated CRS 1018 or CRS 1010. The nonmagnetic members may be fabricated from aluminum or nonmagnetic stainless steel and the bolts may be fabricated from brass or other material having the desired tensile strength and being nonmagnetic.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiments. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a fail-safe permanent magnet lifting device, the combination comprising,

a center pole piece of magnetic amaterial,

a pair of permanent magnets positioned on opposite sides of said center pole piece and having face portions abutting said center pole piece adjacent face portions,

a pair of end pole pieces of magnetic material positionecl on opposite sides of said pair of permanent magnets and having face portions abutting said adjacent permanent magnet face portions,

a coil extending around said center pole piece and connected to a source of direct current through a switchting means operable to energize said coil and to reverse the direction of current ow through said coil,

said center pole piece and said pair of end pole pieces having top Walls arranged in substantially the same plane,

said center pole piece and said pair of end pole pieces having bottom walls arranged in substantially the the same plane,

mechanical means connecting and rigidly securing said end pole pieces, said pair of permanent magnets and said center pole piece to each other as a unitary mass to retain said respective top walls and bottom walls in the same plane,

a keeper plate of magnetic material positioned on the top Walls of said end pole pieces and center pole piece,

said keeper plate having a plurality of apertures therethrough,

said center pole piece having threaded apertures extending downwardly through said top wall in alignment with said apertures 4in said keeper plate,

bolt members extending through said apertures in said keeper plate and threadedly secured in said center pole piece threaded apertures,

said bolts having enlarged head portions spaced :above said keeper plate, and

said keeper plate operable to slide vertically on said v bolts into abutting relation with the underside of said bolt heads to space said keeper plate from said end pole pieces and -said center pole piece and to permit iimited movement of said upper keeper plate relative to said center pole piece to thereby provide an air gap between said center pole piece and said keeper plate.

2. In `a fail-safe permanent magnet lifting device the combination comprising,

-a center pole piece of magnetic material,

a pair of permanent magnets positioned on opposite sides of said center pole piece and having face portions abutting said center pole piece adjacent face portions,

a pair of end pole pieces of magnetic material positioned on opposite sides of said pair of permanent magnets and having face portions abutting said adjacent permanent magnet ace portions,

a coil extending around said center pole piece and connected toa source of direct current through a switching means operable to energize said coil and to reverse the direction of current flow through said coil,

said center pole piece .and said pair of end pole pieces having top walls arranged in substantially the same plane,

said center pole piece and said pair of end pole pieces having bottom walls arranged in substantially the same plane,

mechanical means connecting and rigidly securing said end pole pieces, said pair of permanent magnets and said ceter pole piece to each other as a unitary mass to maintain said respective top walls and bottom Wa'lls in the same planes,

a keeper plate having a pair of elongated members of magnetic material positioned in overlying relation with said end pole pieces and said center pole pieces,

said elongated members hingedly secured to said end pole pieces,

la hook-like lifting device having a stem portion secured in said center pole piece and movable a preselected distance therein,

said stem having an abutment means abutting the underside of said keeper plate elongated members, and

said abutment means operable upon limited movement of said stem portion to move said keeper plate members into spaced relation with said center pole piece.

3. A fail-safe permanent magnet lifting device as set forth in claim 1 in which said permanent magnets each includes a keeper plate magnetically secured to the opposite face thereof.

References Cited UNITED STATES PATENTS OTHER REFERENCES Alpha-Lift, publication by the Great Lakes Supply Co.,

Cleveland, Ohio, January 1965, 4 pp.

lBERNARD A. GILHEANY, Primary Examiner.

50 GEORGE HARRIS, JR., Examiner. 

1. IN A FAIL-SAFE PERMANENT MAGNET LIFTING DEVICE, THE COMBINATION COMPRISING, A CENTER POLE PIECE OF MAGNETIC MATERIAL, A PAIR OF PERMANENT MAGNETS POSITIONED ON OPPOSITE SIDES OF SAID CENTER POLE PIECE AND HAVING FACE PORTIONS ABUTTING SAID CENTER POLE PIECE ADJACENT FACE PORTIONS, A PAIR OF END POLE PIECES OF MAGNETIC MATERIAL POSITIONED ON OPPOSITE SIDES OF SAID PAIR OF PERMANENT MAGNETS AND HAVING FACE PORTIONS ABUTTING SAID ADJACENT PERMANENT MAGNET FACE PORTIONS, A COIL EXTENDING AROUND SAID CENTER POLE PIECE AND CONNECTED TO A SOURCE OF DIRECT CURRENT THROUGH A SWITCHING MEANS OPERABLE TO ENERGIZE SAID COIL AND TO REVERSE THE DIRECTION OF CURRENT FLOW THROUGH SAID COIL, SAID CENTER POLE PIECE AND SAID PAIR OF END POLE PIECES HAVING TOP WALLS ARRANGED IN SUBSTANTIALLY THE SAME PLANE, SAID CENTER POLE PIECE AND SAID PAIR OF END POLE PIECES HAVING BOTTOM WALLS ARRANGED IN SUBSTANTIALLY THE THE SAME PLANE, MECHANICAL MEANS CONNECTING AND RIGIDLY SECURING SAID END POLE PIECES, SAID PAIR OF PERMANENT MAGNETS AND SAID CENTER POLE PIECE TO EACH OTHER AS A UNITARY MASS TO RETAIN SAID RESPECTIVE TOP WALLS AND BOTTOM WALLS IN THE SAME PLANE, A KEEPER PLATE OF MAGNETIC MATERIAL POSITIONED ON THE TOP WALLS OF SAID END POLE PIECES AND CENTER POLE PIECE, 